The invention relates to a control system and method for controlling an engine and in particular to a control system and method for controlling an engine in response to deterioration of the engine. Existing gas turbine engines utilize digital/electronic engine control systems, often referred to as FADEC (Full Authority Digital Electronic Control). These control systems often include mathematical/computational models of various engine systems, sub-systems, and components. These mathematical/computational models are often used to predict and control the behavior of engine systems, sub-systems, and components. Prediction and control of engine behavior may utilize (1) feedback of actual engine behavior by means of sensors located in various parts of the engine (temperature, pressure, speed, etc.), (2) calculations and predictions of engine system, sub-system, and component behavior and (3) schedules describing desired or target system, sub-system, and component behavior under certain engine operating conditions.
Controlling an engine in this manner allows for improved engine performance and efficiency, which provides significant benefits to the customer/user of the engine, such as lower fuel consumption and extended on-wing engine life (the period of time after which the engine must be removed from operation for overhaul/maintenance). These in turn lead to lower operating costs and a wider more flexible range of operational use by the customer/user.
In order to predict and control engine behavior, the mathematical/computational models include information about the physical properties of the relevant engine systems, sub-systems, and components, such as physical size (dimensions, shape), coefficient of thermal expansion, modulus of elasticity, stiffness, time constants, and other physical, mechanical, and thermal properties. This information about physical properties is typically pre-programmed into the engine control system, and represents the physical condition of the engine system, sub-system, or component when new. During engine operation by the customer/user, changes in the physical properties of the engine systems, sub-systems, and components can occur over time. Examples of such changes are wear and distortion, which change the physical size and/or shape of the engine system, sub-system, or component. Such changes in physical properties often reduce or impair engine performance and efficiency, leading to increased fuel consumption, and reducing engine on-wing life. Unfavorable changes of this nature are referred to as deterioration. As an engine deteriorates and undergoes physical changes over time, the physical properties of the deteriorated engine system, sub-system, or components start to deviate from the new physical properties that were pre-programmed into the engine control system. If direct feedback of the changing physical properties from the engine to the control system is not available (as is the case in contemporary engine control a systems), then the control system cannot account for the physical changes. The resulting deviations between the deteriorated physical properties (in the engine), and the new physical properties (in the control system) introduce discrepancies into the mathematical/computational models. These discrepancies impair the ability of the engine control system to accurately predict and control the behavior of the particular engine system, sub-system, or component. This can result in reduced efficiency and on-wing life, increased fuel consumption, and other unfavorable effects on engine performance.
The deviations between deteriorated and new physical properties are most frequently addressed by physical overhaul and maintenance, in which the physical properties are restored from the deteriorated condition to the new condition. This physical maintenance, sometimes referred to as performance restoration, is achieved either by replacement of the particular engine system, sub-system, or component with new hardware, or by physical processing (repair) of the hardware. However, physical overhaul and maintenance of this type is difficult, time consuming, inconvenient, and expensive. An easier, quicker, less expensive, and more convenient method of addressing the control system deviation between the deteriorated and new conditions would therefore be advantageous.
An exemplary embodiment of the invention is directed to a control system for controlling an engine in response to deterioration of the engine. The control system includes a schedule memory for storing a schedule representing target values for a controlled variable. The control system also includes a processor coupled to the schedule memory. The processor receives a reference input and the controlled variable and generates a control signal in response to the reference input and the schedule. The schedule in the schedule memory may be updated to account for engine deterioration so that accurate control is performed. Another exemplary embodiment of the invention is a method for controlling an engine. The method includes updating a schedule to account for deterioration of the engine.